This invention relates to method and circuit arrangement for synchronous detection useful in a digital signal transmission system.
When a digital signal obtained by digital modulating, such as pulse code modulation (PCM), an analog information signal, is transmitted through a transmission line, a synchronous signal word for separating each data from another and a parity word for the detection and correction of errors made during transmission are usually respectively added to data words constituting the digital signal prior to transmission. The synchronous signal word is added to one end of each block having a plurality of data words and a parity word so that it indicates the boundary between two consecutive data blocks in a digital signal. The data word will be detected at a receiving end of a transmission line to distinguish or separate each data block from another. Therefore, in the conventional digital data transmission systems, addition of such a data word has been essential. However, each synchronous data word occupies a given period of time and therefore, addition of such a synchronous signal to data words has been an obstacle to the increase of transmission rate.